Spark gap



June 10, 1969 A. L. MYERS 3,449,614

SPARK GAP Filed Jan. 27, 1967 I I x INVENT OR i/ -g 5,1 J

ATTORNEY United States Patent US. Cl. 313-146 2 Claims ABSTRACT OF THE DISCLOSURE A floating conductor shorter than the distance between end terminals provides either a single long gap or two shorter gaps which break down to provide over voltage protection.

This invention is intended to provide over voltage protection for components of electronic circuits by means of a spark gap type of device which may be connected across the circuit terminals of the component or device to be protected. The spark gap device has an enclosure of insulating material with end terminals and a floating conductor within the enclosure of length shorter than the distance between the terminals. The floating conductor can assume a wide variety of positions from an extreme at which one end of the conductor touches one of the terminals so that there is only a single gap to intermediate positions in which there are gaps between both terminals and the adjacent ends of the conductor.

In the drawing, the single figure is a longitudinal section through the spark gap.

In the drawing, the device, shown some ten times its actual size, has a tubular body 1 of insulating material such as a ceramic having external silvered bands 2, 3 at opposite ends to which are soldered cup shaped end caps 4, 5 telescoped over and closing the ends of the tube -1. The end caps have the usual leads 6, 7 riveted or otherwise secured to the bottom walls of the associated end caps to provide end terminals 8, 9. The terminals 8, 9 are centrally located and are spaced from the inner surface 10 of the tube 1.

Within the tube 1 is an axially slidable elongated conductor 11 having tapered ends 12, 13 respectively presented to terminals 8, 9. The conductor 11 may be made in any suitable manner, for example by stamping from sheet metal. The maximum width of the central section 14 of the conductor 11 is less than the inside diameter of the tube 1 so the conductor is freely slidable lengthwise of the tube and is also free to move radially to some extent. The tube, accordingly, need not occupy the centrally located position shown in the drawing.

The tapered ends of the conductor 11 diverge from the inner surface 10 of the tube and the terminal portions 'ice 15, 16 presented respectively to the end terminals 8, 9 preferably have a width less than the width of the associated end terminal so that in all positions of the conductor 11, the sections 15, 16 will always be remote from the inner surface of the tube and presented to the associated end terminal. Under some conditions, the section 15 of the conductor 11 may be in direct contact with the terminal 8 (or 9), providing a single large gap between the section 16 (or 15) and the terminal 9 (or 8). More commonly, it is expected that the conductor 11 will occupy an intermediate position in which there are two spark gaps, one between the terminal 8 and section 15 and the other between terminal 9 and section 16. Whether there are one or two gaps, the breakdown voltage is essentially the same.

The spark gap is intended to provide high energy absorption and reliable breakdown voltage. The sparking always takes place between metal parts, thereby avoiding tracking of the insulating material 1 which could affect the reliability. The enclosure provided by the end caps 4, 5 seals the interior of the tube from outside contaminants. The breakdown voltage is readily controlled by the spacing of the end caps. This permits a wide range of voltage ratings from the same physical parts.

What is claimed as new is:

1. A spark gap device comprising a tubular body of insulating material, axially spaced terminals fixed to the body and presented toward each other, a conductor axially slidable in the body between the terminals and having opposite ends respectively presented to one and the other of the terminals, the length between opposite ends of the conductor being less than the space between the terminals whereby in any position of the conductor at least one spark gap is provided between one terminal and the end of the conductor adjacent said one terminal, the conductor having tapered ends diverging from the inner surface of the tube to reduce sections adjacent the terminals so that in all positions of the conductor the reduced sections are opposite the adjacent terminals and remote from the inner surface of the tube.

2. The spark gap of claim 1 in which the conductor is of metal having a thickness small compared to the length and width of the conductor.

References Cited UNITED STATES PATENTS 12/1942 Watson 313l46 12/1953 Stoelting 313146 US. Cl. X.R. 3 13325 

